Percussion devices often comprise a linearly working percussion piston that is controlled by a slide valve. Usually the slide valve is controlled by a signal channel whose pressure varies. Either a tank pressure or full working pressure acts upon the transition surface of the slide valve via the signal channel.
Usually the seal between the pressure channel and the tank channel consists of only a radial column seal where there will always be some play, and which can give rise to leakage and decreased efficiency. The slide valve can also drift during the percussion piston's displacement and provide an even shorter column seal length.
U.S. Pat. No. 4,142,447 discloses a percussion device that comprises a slide valve and a plurality of pins that are arranged in a machine housing to press against an upper end of the slide valve and thereby hold the slide valve in place in its lowermost turning location. The upper end of the pins is subjected to the pressure in a pressure chamber that is arranged inside the machine housing.